OTMA lightweight transaction pipe enhancement

In IMS 15, the OTMA lightweight transaction pipe enhancement improves the flood control of OTMA transaction pipes (tpipes).

This enhancement is added to IMS 15 by APAR PH17832 (PTFs UI68699 and UI68700).

Previously, when a back-end IMS system processed OTMA input transactions from front-end IMS systems in a shared queues environment, each transaction might trigger the creation of a new tpipe. However, if a tpipe is built for input messages, the output ITASK for the tpipe is not used. If a tpipe is built for output processing, the input ITASK is not needed. Such insufficient use of resources associated with a tpipe makes the back-end IMS system easily reach the limit of tpipe flood.

By using the OTMA lightweight tpipe function, IMS reduces the storage for each tpipe by dynamically allocating the associated ITASKs and other tpipe related storage only when they are needed. By doing so, the back-end IMS system in a shared queues environment can support more tpipes and avoid reaching the tpipe flood limit quickly.

Changes to system definition for IMS

A new parameter LITETP= is added to the DFSOTMA descriptor in the DFSYDTx member of the IMS.PROCLIB data set to specify whether the OTMA lightweight tpipe function is enabled. You can enable the OTMA lightweight tpipe function by specifying LITETP=YES. The default is NO, which is also the default for an IMS cold start.

Specifying LITETP=YES enables IMS to support more tpipe because a lightweight tpipe requires less storage than a regular tpipe. A weighting factor is used on lightweight tpipes when calculating the tpipe count for tpipe flood control. The weighting factor is the percentage of the lightweight tpipe storage size relative to the regular tpipe storage size, which is usually 28%.

The adjusted tpipe count is calculated as follows:
  • A: the number of front-end tpipes (total tpipes - back-end tpipes)
  • B: the number of back-end tpipes
  • W: the weighting factor
  • adjusted tpipe count=A+(B*W)

When the DFSOTMA MAXTP= parameter is specified, if the LITETP= parameter is enabled, IMS monitors if the number of tpipes reaches the maximum allowable number by using the adjusted tpipe count instead of the total tpipe count. If the LITETP= parameter is disabled, IMS keeps using the total tpipe count for flood control.

Changes to troubleshooting for IMS

For a list of the messages and codes that are new or changed for this enhancement, see the IMS messages and codes row in the table in Documentation changes.

For a complete list of all of the new, changed, and deleted messages, and abend codes in IMS 15, see Message and code changes in IMS 15.

Changes to commands

The /DISPLAY command is enhanced to display two new output fields BETP (back-end tpipe) and WGF (weighting factor).
BETP
If LITETP=YES is specified in the DFSOTMA descriptor, this field shows the number of back-end tpipes for the OTMA member. Otherwise, it is zero.
WGF
The tpipe weighting factor for calculating the adjusted total tpipe count for detecting flood condition. A value of 0 indicates that the OTMA lightweight tpipe function is disabled.

The TOACEE output field is changed to TOA.

For a list of the commands that are new or changed for this enhancement, see the IMS commands row in the table in Documentation changes.

Documentation changes

The following table lists the publications that contain new or changed topics for the OTMA lightweight transaction pipe enhancement enhancement. Publications that are not impacted by this enhancement are not included in the table.

Table 1. Links to topics that have new or changed content for this enhancement
Publication New or changed topics
Release planning
System definition
Communications and connections
  • Open Transaction Manager Access (OTMA)
IMS messages and codes
IMS commands